//1.同步版分步加法
function doStep1(init){
    return init + 1;
}

function doStep2(init){
    return init + 2;
}

function doStep3(init){
    return init + 3;
}

function doOperation(){
    let result = 0;
    result = doStep1(result);
    result = doStep2(result);
    result = doStep3(result);

    return `同步版结果：${result}`;

}


//2.异步版
function asyncDoStep1(init,callback){
    const result = init + 1;
    callback(result);
}

function asyncDoStep2(init,callback){
    const result = init + 2;
    callback(result);
}

function asyncDoStep3(init,callback){
    const result = init + 3;
    callback(result);
}

//回调:"回调地狱"
 function asyncDoOperation(out){
    asyncDoStep1(0,result1 =>{
        asyncDoStep2(result1,result2 =>{
            asyncDoStep3(result2,result3 =>{
                out.innerHTML += `异步版结果：${result3}`
                // return `异步版结果：${result3}`;
            })
        })
    })
}